1. Field of the Invention
The present invention relates generally to monitoring of digital communication networks. More specifically, a system and method for automated monitoring of availability in xDSL access networks are disclosed.
2. Description of Related Art
An Internet user typically accesses the Internet by subscribing to an Internet Service Provider (“ISP”). The ISP accesses the Internet and transmits desired Internet content between the Internet user and the Internet content provider. The Internet user may also subscribe to high speed access to provide connection between the subscriber or client and the ISP to which the client subscribes. One example of high-speed access is via a digital subscriber line (“DSL”). DSL is generally provided by means of a connection-oriented packet network that provides connectivity among remote users or client premises and the Internet via ISPs. In a packet-based switching network, data is transmitted between the Internet content provider and a customer premises equipment (“CPE”), e.g., a modem, at the Internet user's site.
The connection-oriented packet network includes a DSL loop using a pair of twisted copper telephone lines extending between the CPE and a central office (“CO”) of a telephone company such as an incumbent local exchange carrier (“ILEC”). Both competitive local exchange carriers (“CLECs”) and ILECs can provide DSL service to clients. The connection-oriented packet network may further include ATM or Frame Relay switches. The network switches facilitate establishment of virtual circuits (“VC”) between each client and the ISP to which the corresponding client subscribes The VC between each client and the ISP to which the corresponding client subscribes establishes connectivity between each client and the Internet via the respective ISP.
There are various types of DSL technologies with differing distance and bandwidth characteristics that provide connection-oriented packet connectivity. These various types of DSL are typically referred to as xDSL and may include, for example, asymmetric DSL (ADSL), symmetric DSL (SDSL), ISDN DSL (IDSL), high-speed DSL (HDSL), HDSL2, symmetric HDSL (SHDSL), very high-speed DSL (VDSL), as well as other emerging DSL technologies.
FIG. 1 is a block diagram illustrating an exemplary architecture for an xDSL access network 100. At a customer premise 104, a computer or PC 102 is in communication with a CPE 106 such as a DSL modem. The DSL modem 106 is in communication with a DSL access multiplexer (DSLAM) 108 located at a local CO over a pair of twisted copper telephone lines 110. Typically, several DSLAMs in a region are connected to a switch in a network access provider (NAP) backbone 112. The NAP backbone 112 may utilize any suitable wide area network (WAN) technology such as asynchronous transfer mode (ATM), synchronous optical network (SONET) or synchronous digital hierarchy (SDH), frame relay, T1, E1, T3, or E3. The NAP backbone 112 in turn aggregates user connections to a broadband remote access server (BRAS) 114 coupled to a Remote Authentication Dial-In User Service (RADIUS) server 118 in a PoP 116, typically managed by the NAP. The BRAS 114 is connected to a public network 120 such as the Internet which in turn provides connectivity to various network service providers (NSPs) 122. As is evident, the NAP typically owns and manages the transport networks that provide connectivity between the customer premises 104 and NSPs 122.
Typically, it is desirable for the NAP to monitor the quality of service (QoS) in the access network for various purposes such as performance evaluation and enhancement, as well as proactive reporting of service level agreement (SLA) compliance to partners and customers. One important metric of QoS is network availability, requiring regular periodic measurements. However, it is often difficult to effectively measure and monitor network availability in xDSL access networks due, at least in part, to the heterogeneous nature of xDSL access networks, which comprise various types of network technologies. Correlation of failure events across DSLAMs, Frame Relay/ATM switches, and BRAS devices to assess network unavailability in such large networks is impractical. In addition, utilizing the customer premises equipment, such as the DSL modem or the customer's computer, as a reference point for monitoring network connectivity on a regular basis is ineffective as the NAP typically does not control the CPE, which may be powered off at times by the end-user. Furthermore, the large and growing broadband subscriber base renders such an approach inefficient.
Service Level Agreements (SLAs) are generally contracts between service providers and customers that specify performance guarantees associated with various QoS metrics such as network availability, latency, and/or packet loss. SLAs often also specify penalties, typically in the form of rebates or credits, for failure to meet those performance guarantees.
Conventionally, monitoring of network availability for SLA compliance in homogenous layer 2 networks, such as ATM WANs, is performed by transmitting operations, administrations, and maintenance (OA&M) loopback cells on a periodic basis to verify network connectivity.
As another example, ping packets may be utilized to monitor network availability in networks based on the Internet Protocol (IP). The ping packets test connectivity between two points at regular intervals using Internet Control Message Protocol (ICMP) echo/reply. However, there are several drawbacks associated with the use of ICMP packet for monitoring the availability in networks. In particular, ping packets are generally given low priority in network devices such as routers and BRAS, as compared to high priority user or management traffic. Consequently, ICMP packets may be dropped or discarded during periods of greater network traffic or network congestion even when connectivity across the network is up. Thus, a lower than actual measure of network availability may result.
In addition, routers may block or rate-limit ICMP packets, including ping packets, because they can be easily utilized in certain security attacks. An example of such a security attack is a denial-of-service attack in which a large number of ping packets are sent to a network device, degrading its performance for user applications. Thus, the blocking or rate-limiting of ICMP packets at routers may adversely impact the results of connectivity or availability tests and monitoring.
Furthermore, ping packets are typically sourced from and targeted at network devices that support TCP/IP. Thus, DSL modems that are bridges and most DSLAMs are generally excluded from being a source or target of ping packets. Moreover, ping packets do not contain time-stamps that are typically required for monitoring the duration of connectivity loss.
Thus, what is needed is a system and method for a more efficient, convenient, and effective monitoring of the availability of xDSL access networks, thereby facilitating comparison of actual availability to that specified in a Service Level Agreement (SLA) with customers. Ideally, the system and method provides measurements that are independent of the type of user application.